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RESEARCH PAPERS

J. Eng. Mater. Technol. 1987;109(4):259-265. doi:10.1115/1.3225974.

Available experimental data from uniaxial tests are analyzed to estimate values for parameters of a microcrack dependent model of material response. The experimental data on microcrack density evolution during uniaxial deformation were obtained with small-angle X-ray scattering techniques on polymer specimens. The parameters of the microcrack dependent model are the opening and size of the microcracks, a thermodynamic potential for microcrack kinetics that describes energy conditions for microcrack creation, and coefficients in a nonlinear Onsager type relationship to describe rate kinetics of microcrack creation. The Onsager relationship contains a nonequilibrium thermodynamic measure that is the work done per microcrack created minus the thermodynamic energy per microcrack created. Deformation stability concepts of microcrack dependent material response are discussed in terms of mechanical stability, thermodynamic stability, and global or system stability of the uniaxial test.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):266-271. doi:10.1115/1.3225975.

The dynamic compaction processes of copper powder which was filled in two layers into a die and subjected to solid punch impaction were investigated experimentally in order to assess the effect of different initial density distributions of the powder on the compaction process. The compaction experiments were performed for two situations of layer arrangement: in the first situation the upper layer had a lower uniform initial density distribution than the lower layer and in the second this order was reversed. The processes were photographed for the two situations of layer arrangement using a high speed camera in order to analyze the movement of powder medium and punch, the propagation of shock and elastic waves in the powder medium and density distributions. The pressure on the plug supporting the medium in the die was also measured so that the analysis of the photograph would be facilitated. The two compaction processes observed and analyzed differed considerably, but the green density distributions had only a slight difference. The compaction process obtained for the first situation of layer arrangement agreed well with the theoretical prediction reported previously by the authors. The compaction process for the second situation also agreed with the theoretical result, indicating that the amounts of internal energy dissipation during the two processes differ only slight.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):272-275. doi:10.1115/1.3225976.

An analysis of the stress-strain curves superposition method for the evaluation of the average deformation ε and redundant deformation factor φ is presented. This approach, originally proposed by Hill and Tupper, makes unrealistic suppositions, which led to some confusion in the literature concerning curve superposition criteria; the values of φ depend on the material, contrarily to Hill and Tupper’s original idea. If the technique is to be used, it is necessary to establish clear and objective superposition criteria.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):276-281. doi:10.1115/1.3225977.

Based on a previous literature analysis of the stress-strain curves superposition method for the evaluation of the redundant deformation factor φ, an experimental program is proposed and carried out for SAE 1018 steel. The method is applied for tensile and compressive testing, and for multiple and single passes up to 30 percent logarithmic strains. For single passes, results for tensile testing were reasonably in accordance with those in the literature. For multiple passes, work hardening was higher for 2 or 3 passes than for 1 pass, contrarily to results for Copper in the literature. Compression testing should not be used for φ evaluation if one wants to obtain φ values similar to those in the literature.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):282-287. doi:10.1115/1.3225978.

In practical applications of laser drilling the quality of the drilled hole is the critical factor, and recently methods of studying the influence on quality of the main process variables have been developed, which seek to improve quality rather than explain the drilling mechanism. Hole quality can be judged by: internal form and taper and related geometrical features, and the extent of heat affected materials. The optimum performance in laser drilling depends very much upon the proper selection of laser parameters as well as the physical properties of the workpiece material. With so many variables, and incomplete knowledge of the relationships between them, statistical methods are needed to design experiments and analyze the results. In the present work five factors at four levels were considered. Four factors are given quantative; one, the material specification, is qualitative. The result is that the design has four blocks indentified with materials each of which can be treated as a complete factorial design. However, the materials can be described quantitatively by their physical properties, so the results were correlated with the groups generated by the dimensional analysis. It is observed that main effects of laser parameters as well as their interactions, have significant effects on all features of hole geometry. Drilling medium pressure was found to be very effective factor, since its interactions with the other parameters in any order are significant.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):288-292. doi:10.1115/1.3225979.

This paper presents the results of both experimental and analytical investigations into the conditions of failure for lamellar-graphite case iron under various modes of loading. The orientation of fracture planes is experimentally determined and surfaces of fracture zones are carefully examined with the help of a scanning electron microscope. While fracture for a tensile test takes place along its cross section, fracture in the compression test is herein shown to insist on developing along a plane inclined at some 55 to 65 deg to the cross section, irrespective of notches or grooves intentionally machined to persuade fracture to pursue certain preassigned paths. For the case of uniaxial compression, the present analysis correlates the ratio of compressive to tensile strengths to both rupture and friction angles. Relevant values are in conformity with earlier findings.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):293-298. doi:10.1115/1.3225980.

Two multiaxial fatigue damage models are proposed: a shear strain model for failures that are primarily mode II crack growth and a tensile strain model for failures that are primarily mode I crack growth. The failure mode is shown to be dependent on material, strain range and hydrostatic stress state. Tests to support these models were conducted with Inconel 718, SAE 1045, and AISI Type 304 stainless steel tubular specimens in strain control. Both proportional and non-proportional loading histories were considered. It is shown that the additional cyclic hardening that accompanies out of phase loading cannot be neglected in the fatigue damage model.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):299-305. doi:10.1115/1.3225981.

Current development of Advanced Steam Cycle coal-fired power plants requires superheater and reheater tubing alloys which can withstand severe conditions for high temperature corrosion. A corrosion equation to predict corrosion rates for candidate alloys has been developed by a study of deposits removed from steam generator tubes and from test probes installed in a boiler, supplemented by laboratory studies using synthetic coal ash. The corrosion equation predicts corrosion for a particular coal as a function of its content of sulfur, acid-soluble alkalies, and acid-soluble aklaline earths. Good agreement was obtained between the corrosion equation and 6000-hour tests using probes of TP347H and 17-14 CuMo.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):306-313. doi:10.1115/1.3225982.

The similarity of dynamic compaction processes was investigated theoretically and predicted in our previous report, where powder media in a die were assumed to be of a simple type, and the punch and plug to be rigid bodies. The predictions were based on a set of one-dimensional equations and a set of nondimensionalized one-dimensional equations. The objective of this study is to examine the similarity experimentally and to present the results of compaction experiments in order to verify the existence predicted. The experiments were carried out on a copper powder medium in dies having inner cross-section in elementary shapes such as circle, square and triangle. The pressure of the medium at a point contacting the end of the plug, the density distribution and mean density of the green compacts were measured in the experiment. From the analysis of the experimental data the validity of the dynamic similarity theory was demonstrated and the similarity was verified to exist despite the differences in size and shape between the dies used, which implies that the copper powder medium in the dies of elementary shapes is of a simple type. Relations between the density and the shape coefficients showed that the density reached maximum as the coefficients decreased approaching a certain point with a decreasing influence of the die wall friction, while past that point, contrary to the prediction by the theory, it began to decrease due to an increasing influence of the elastic deformation of the punch and plug.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):314-318. doi:10.1115/1.3225983.

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):319-325. doi:10.1115/1.3225984.

The upper limit of steam temperature which 12Cr steel rotors can withstand has been considered to be 566°C, but the recent projects on the advanced steam turbine of large capacity demand to raise it. The key factor in upgrading the creep rupture strength of the existing 12Cr steel rotors is to adjust “Equivalent Molybdenum Content” to the optimum, which is 1.5 percent in case no tungsten is contained. A HP-IP rotor, of 11 tons in final machined weight, for EPDC’s Wakamatsu high-temperature turbine to be operated with 593/593°C steam, has been manufactured with the chemical composition of C 0.14, Si 0.08, Mn 0.51, P 0.013, S 0.001, Ni 0.60, Cr 10.23, Mo 1.48, V 0.17, Nb 0.056, N 0.045, and Al 0.002 percent, respectively, through ESR process, Its creep rupture strength after heat treatment is 122 MPa for 593°C and 105 hr. The paper reports the concept of this material and the actual achievement in Wakamatsu rotor forging, referring to the working condition expected on the rotors for 1000 MW-class advanced steam turbine.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):326-336. doi:10.1115/1.3225985.

This paper is concerned with the behavior of metallic materials under general complex loadings. A complete experimental investigation is carried out to exhibit the main features of this behavior. Nonproportional loadings are characterized by an additional hardening when compared to proportional loadings. This hardening is observed to be strongly dependent on the loading path and can be recovered when the nonproportionality decreases. It is shown that a classical model of elasto-viscoplasticity fails when applied to the prediction of responses under complex loadings. The examination of the assumptions on which the model is built allows to understand its deficiencies and, on the basis of an experimental program, a simple constitituve model is derived for cyclic elastoviscoplasticity under nonproportional loadings. This model is shown to give good results for the prediction of very complex tests.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):337-342. doi:10.1115/1.3225986.

A method based on fracture mechanics solutions for a circumferential crack is used to measure the distribution of axial residual stresses in the circumferential weld between two cylinders. The case considered is a 22 pass weld and the residual stress is obtained in the form of a Legendre polynomial series. The results are in general agreement with published values for multi-pass welds on similar material. However, the present approach appears to be considerably simpler and easier to implement than existing experimental methods.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):343-349. doi:10.1115/1.3225987.

The effect of constitutive modelling of material behavior on the predictive abilities of two models of flat rolling is studied. Comparison of calculated roll forces and powers to those measured on a commerical steel mill indicates that the Orowan model is sufficiently accurate when supplied with carefully determined flow strength data. The manner of representation of that data is found to be significant. The results show that a multidimensional databank, which stores values of strength for specific strains, rates of strain and temperatures is very useful in modelling the process.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Eng. Mater. Technol. 1987;109(4):350-352. doi:10.1115/1.3225988.

The double ligament tensile (DLT) test was used to evaluate the tensile properties and anisotropy of a lithium-containing aluminum alloy in the three orthogonal directions of the wrought ingot metallurgical plate. In order to minimize uncertainties associated with results obtained from this test comparisons are made with results obtained from the conventional tensile test. Variation in tensile properties with direction of stressing are discussed in terms of the specific role of specimen size and configuration, and intrinsic microstructural features.

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Eng. Mater. Technol. 1987;109(4):353. doi:10.1115/1.3225989.
FREE TO VIEW
Abstract
Topics: Grinding
Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):353. doi:10.1115/1.3225990.
FREE TO VIEW
Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1987;109(4):354. doi:10.1115/1.3225991.
FREE TO VIEW
Commentary by Dr. Valentin Fuster

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